The present invention is directed to integrated circuits and, more particularly, to a capacitance sensor circuit with noise rejection.
Capacitance sensors can be used to detect or measure variation of capacitance at a capacitive touch panel interface. Common examples of capacitive interfaces are touchpads and touchscreens. In a capacitive touch interface, proximity of an electrically conductive object, such as a human finger or conductive stylus, alters electric fields in the touch interface. The capacitance sensor can sense or measure the physical position or movement of the object relative to the interface and provide a corresponding analog or digital code output signal.
Capacitive interfaces have a matrix of capacitance elements. Sensing the variations of capacitance in the interface is subject to perturbations, referred to as noise, which may be due to conduction from a power supply or adjacent circuit elements, or induced by external radiation. The noise may be at frequencies higher or lower than the operating frequency of the capacitance sensor.
It would be advantageous to have a capacitance sensor with a high level of noise rejection, suitable especially for use in noisy environments.